Some organisations use significant amounts of water that never enter the public sewer. Find out how a Non-Return to Sewer allowance may affect wastewater charges.
How are sewerage charges calculated?
When an organisation receives a metered water supply, its wastewater volume charges will usually be linked to the amount of water recorded by the incoming water meter.
That is understandable as a starting point. However, it does not necessarily mean that every cubic metre of water entering the premises subsequently enters the public sewer.
Water may evaporate, become part of a manufactured product, be used for irrigation, be consumed by livestock or be removed from the site by an alternative route. Where the amount not returned to sewer is greater than the allowance already incorporated into the charging arrangement, there may be grounds to request an additional Return to Sewer allowance, commonly described as a Non-Return to Sewer allowance or NRTS.
Current industry good-practice guidance states that sewerage wholesalers apply a default Return to Sewer percentage of 95% to metered sewerage volume charges. This has the effect of recognising, through a standard 5% allowance, that not all water supplied will return to the sewer. An additional allowance may be considered where the organisation can demonstrate that its actual non-return is greater than that default allowance.
What does Non-Return to Sewer mean?
Non-Return to Sewer refers to water that is recorded as entering a premises but does not subsequently discharge into the public foul sewer.
Wastewater volume charges are often calculated by applying a Return to Sewer percentage to metered water consumption. For example, a 95% Return to Sewer percentage means that wastewater volume charges are calculated on the assumption that 95% of the metered water returns to the sewer, with the remaining 5% already recognised as not returning.
An additional NRTS allowance does not normally mean that an organisation receives credit for all water that fails to return to sewer. The standard allowance already included within the charging arrangement must be taken into account. The additional adjustment is therefore concerned with the evidenced non-return above the applicable default position.
For example a Non-Return to Sewer claim form, will be used to calculate the claimed non-return percentage and then as part of calculations deduct the standard 5% allowance when establishing the net additional amount claimed.
Why might water not return to the sewer?
The physical route taken by water depends on the premises, its activities and its drainage arrangements. Recognised examples include the following.
Evaporation
Water may evaporate through:
Cooling towers
Boilers and steam systems
Heated swimming pools
Laundries
Industrial heating or cooling processes
Industry guidance specifically identifies boilers, cooling towers, heated swimming pools and laundries as activities where evaporation may cause water not to return to sewer.
Water incorporated into a product
Some of the incoming water may become part of what an organisation manufactures or supplies. Examples can include:
Food and drink manufacturing
Bakeries
Cement and concrete production
Chemical or pharmaceutical processes
Other water containing products
Both market guidance and retailer information identify water added to a product as a potential basis for an additional Return to Sewer allowance.
Irrigation and grounds maintenance
Water used to irrigate landscaped areas, crops, playing fields, golf courses, plant stock or other outdoor areas may not enter the foul sewer.
This could be relevant to organisations such as:
Garden centres
Golf clubs
Sports facilities
Schools and academies with extensive grounds
Hospitality and leisure sites
Agricultural or horticultural businesses
Public bodies responsible for maintained land
An allowance should not be assumed simply because water is used outdoors. The organisation would still need to establish the volume involved and show that the relevant water does not enter the public sewer.
Water removed from the site
Water or wastewater may sometimes be collected and lawfully removed from the premises rather than discharged into the public sewer. Supporting evidence could include:
Waste transfer or disposal records
Tankering records
Contractor invoices
Collection records
Volumes recorded by suitable meters
Details of the receiving disposal facility
The treatment of occasional off-site disposal can differ from an ongoing percentage based allowance. For example, Anglian Water Wholesale’s published allowances policy separately describes sewerage abatements for one off events where material is tankered and disposed of elsewhere, requiring evidence of the volume and proof of disposal.
Livestock and agricultural use
Water consumed by livestock, used in certain agricultural activities or otherwise retained away from the public sewer may also be relevant. Current industry good practice guidance includes drinking water for livestock and agricultural use among the recognised reasons why water may not return to sewer.
Which organisations should consider reviewing NRTS?
An NRTS review may be worth considering where an organisation:
Uses substantial volumes of water in production
Operates cooling towers, steam systems or evaporative equipment
Manufactures food, drink or another water containing product
Irrigates large grounds, sports pitches or landscaped areas
Operates a swimming pool or leisure facility
Uses water for horticultural or agricultural purposes
Removes wastewater or process material from the site
Has installed water reuse or water recovery systems
Has a site process that creates a clear difference between incoming water and sewer discharge volumes
The important question is not simply whether some water fails to return to sewer. A default allowance is already incorporated into the standard charging basis. The more useful question is:
Does the amount of water demonstrably not returning to the public sewer materially exceed the allowance already recognised in the wastewater charges?
How is an allowance established?
A successful application normally needs to do more than describe the business activity. It must provide a reasonable and supportable method of quantifying the water that does not return to sewer.
Sub-metering
In many cases, sub-metering provides the clearest evidence. A private meter might measure:
Water supplied to an irrigation system
Water entering a manufacturing process
Cooling tower make-up water
Water transferred into a storage tank
Water going to another separately identifiable use
The quantity actually discharged to sewer
The current good practice guide states that wholesalers may require private sub-meters, together with information such as the meter’s make, model, serial number, installation date, initial reading and location. It also states that requested private meters must meet the requirements of the Measuring Instruments Regulations 2016.
The cost, installation, maintenance and ongoing reading of a private sub-meter will generally need to be considered by the customer.
A site water balance
A water balance compares the total volume entering a site with the different ways in which that water is used or discharged.
A simplified water balance might include:
Incoming metered water
Domestic use by employees and visitors
Production use
Water contained in finished products
Evaporation
Irrigation
Off-site disposal
Trade effluent discharge
Other discharge to the foul sewer
The total allocation should reconcile sensibly with the incoming volume. Current market guidance specifically recommends that customers provide a simple water balance explaining how and where water is used and whether it returns to sewer.
Supporting operational information
Where direct measurement is not practical, a wholesaler may consider other evidence. Depending on the activity, this could include:
Production volumes
Product recipes or water content information
Equipment specifications
Evaporation calculations
Irrigation records
Staff or visitor numbers
Tankering records
Waste transfer documentation
Site plans and drainage plans
Photographs
Main-meter and sub-meter readings
Whether calculated evidence will be accepted depends on the relevant wholesaler’s policy and the reliability of the proposed methodology. Anglian Water Wholesale, for example, states that where metering is not practical or economically viable, an allowance may be considered when strong evidence and a supporting calculation methodology are provided.
Who makes the application?
In the English non-household market, the customer would normally contact its retailer. The retailer then assesses and submits the allowance request to the sewerage wholesaler on the customer’s behalf.
The wholesaler considers the evidence, may request further information or arrange a site visit, and informs the retailer of its decision and the date from which an approved allowance applies. If changes to an allowance are made, the wholesaler will then update the central market systems with the correct allowance which the retailer is then responsible for reflecting the approved position in the customer’s charges.
This distinction matters because the organisation may receive its bill from a retailer, while the sewerage wholesaler’s policy determines whether and how the underlying allowance is approved.
Are all wholesaler policies the same?
No. The industry guide is intended to encourage consistency, but it expressly recognises that individual wholesaler policies and practices can differ and may change over time. The current policy should therefore be checked before an application is prepared.
Differences may include:
The evidence required
Whether a sub-meter is expected
How calculated evidence is assessed
The application process used by the retailer
The effective date of an approved allowance
The treatment of retrospective periods
How frequently an allowance is reviewed
Ongoing meter reading requirements
What happens when the process or occupier changes
For example, Anglian Water Wholesale’s published policy requires periodic meter information for metered allowances and states that its allowances are reviewed every two years, while the Wave (retailer) Return to Sewer guidance asks eligible customers to reapply annually and recommends monthly sub-meter readings. These examples reinforce the need to check the arrangements relevant to the specific account rather than assuming that one policy applies nationally.
Can an allowance be backdated?
Backdating should never be assumed.
The effective date depends on the applicable wholesaler policy, the circumstances and the quality and timing of the available evidence. Some policies distinguish between a first time application, correction of an allowance removed in error and a change to an established allowance supported by historical readings.
For instance, Anglian Water Wholesale’s published policy states that evidence supporting a first time change from its standard position is applied going forward rather than retrospectively. It describes different arrangements where an existing allowance was reset in error or where historical evidence supports a change to an existing allowance.
Organisations should therefore avoid assuming that identifying a potential historical discrepancy will automatically produce a retrospective credit.
What happens if the business changes?
An NRTS allowance is based on particular operational circumstances. It may cease to be representative if:
Production volumes change
A manufacturing process is altered
Irrigation requirements reduce or increase
Equipment is replaced
A sub-meter fails
Drainage arrangements change
An occupier changes
Water begins to enter a different discharge route
Additional water sources are introduced
Current good practice guidance says customers should inform their retailer of significant changes that may affect the allowance. It also provides for review by the customer, retailer or wholesaler.
An allowance should therefore be treated as an evidence based charging arrangement that requires continuing oversight, not as a permanent exemption.
What about trade effluent?
Trade effluent charging requires particular care.
Where trade effluent charges apply, the wholesaler’s trade effluent team will normally consider relevant non-return volumes when calculating the trade effluent volume or basis of charge. An organisation should avoid assuming that an NRTS adjustment can simply be applied independently of the trade effluent calculation.
The incoming water meter, foul sewerage charges, trade effluent volumes and any water supplied from alternative sources may need to be considered together. Current guidance also notes that a wholesaler may charge for sewer discharges arising from alternative sources, such as a borehole or rainwater harvesting system.
A practical starting checklist
Before approaching the retailer, it can be helpful to establish:
Which organisation is the sewerage wholesaler?
What Return to Sewer percentage is currently applied?
Is an additional allowance already recorded?
Which activities cause water not to enter the sewer?
Can those volumes be measured directly?
Are suitable sub-meters already installed?
Are reliable main-meter and sub-meter readings available?
Can a site water balance be prepared?
Are drainage plans, production information or disposal records available?
Does trade effluent charging also apply?
Has the site, process or occupier changed since any existing allowance was agreed?
What does the applicable wholesaler’s current policy require?
A clear evidence pack prepared around these questions is more persuasive than a broad statement that the organisation “uses a lot of water outside”.
How WTR Utilities can help
WTR Utilities can independently review the available water and wastewater information to help establish whether the current charging basis appears consistent with the way water is actually used at the premises.
Depending on the agreed scope, this may include examining:
Water and wastewater bills
The Return to Sewer percentage currently applied
Meter and sub-meter information
Site processes and operational records
Evidence of water incorporated into products
Irrigation or evaporation information
Drainage arrangements
Trade effluent interactions
Available wholesaler policies
The information that may be needed to support further enquiries
The purpose is not to assume that an allowance is due. It is to establish the facts, identify any material difference between the assumed and evidenced sewer return and help the organisation determine whether a properly supported application is justified.
Do your wastewater charges reflect what actually returns to the sewer?
If a material proportion of your water is used in production, irrigation, evaporation or another non-sewer activity, an independent review can help you understand the current charging position and the evidence that may be required.
Important information: This article provides general information about non-household water and wastewater charging arrangements in England. It does not confirm that any organisation is entitled to an allowance, adjustment, refund or retrospective credit. Eligibility, evidence requirements, effective dates and review arrangements depend on the relevant wholesaler’s current policy, the retailer’s processes and the specific circumstances of the premises.